Data-Over-Cable Service Interface Specifications (“DOCSIS”) has been established by cable television network operators to facilitate transporting data traffic, primarily internet traffic, over existing community antenna television (“CATV”) networks. In addition to transporting data traffic as well as television content signals over a CATV network, multiple services operators (“MSO”) also use their CATV network infrastructure for carrying voice, video on demand (“VoD”) and video conferencing traffic signals, among other types.
In transporting downstream multimedia content, as well as data, an upstream message, or messages, is/are typically sent to request the content and to set up a service flow to deliver the content. In addition to downstream multimedia content, such as video, voice traffic also uses message signaling to set up service flows for the upstream and downstream directions.
These signals are typically sent over a fiber network to a location, sometimes referred to as a node, near an end user, and from the node to a broadband user's device via a coaxial cable. Such an arrangement is known in the art as a hybrid fiber coaxial network (“HFC”).
Conventionally, a cable modem termination system at an MSO's headend converts information to quadrature amplitude modulation (“QAM”) symbols for transmission over a radio frequency channel to user devices such as cable modems. The collecting, processing and modulating of downstream signals is traditionally performed by the same physical unit at the CMTS, often the circuitry is all contained on the same silicone chip.
However, for cost and scaling reasons, it may be desirable to have traditional CMTS switching functionality separated from downstream modulation and upconverter circuitry, with the modulation circuitry communicating with the CMTS via a convenient interface, such as, for example, a gigabit Ethernet link. The upstream switching functionality is performed at the CMTS and the downstream modulation is performed at a node device, herein referred to as an EdgeQAM device that is remotely located downstream from the CMTS. Both the CMTS and the remotely located edgeQAM device typically have their own dedicated clocks. To ensure synchronicity between downstream traffic and upstream traffic when a CMTS serves multiple edgeQAM devices, especially when using synchronous code division multiple access technology in the upstream direction, there is a need in the art for a method and system for synchronizing the clock at the CMTS and the one or more edgeQAM devices that are coupled with the CMTS.